Friday, February 02, 2007

Fourth Assessment Report of the IPCC

The key diagram is on the last page, p21. This shows the predicted evolution of global temperature over the course of the 21st century, for the six SRES 'marker' scenarios. By taking an average over the output of the various different global climate models, each differently coloured line represents the predicted evolution of global temperature under a particular scenario. Scenarios prefixed with an 'A' are scenarios in which economics are the driving factors, whereas scenarios prefixed with a 'B' are scenarios in which environmental policies are the driving factors. A1FI is the scenario in which fossil fuels continue to dominate global energy consumption, A1B is the scenario in which fossil fuels reach a balance with renewable energy sources, and A1T is the scenario in which there is a transition between fossil fuel usage and renewable energy.

The cost of solar energy is halving each decade, and solar energy is predicted to become a competitive rival to fossil fuel circa 2030-2040. Accordingly, the A1T scenario used in the third IPCC assessment report in 2001 represented CO2 emissions to decline beyond 2040. Assuming that economics will continue to be the driving factor, the two most realistic scenarios are therefore A1T and A1B. The scenario which produces the highest estimated rise in global temperatures, the A1FI scenario, is technologically and economically unrealistic, so the upper limits of the IPCC temperature range can be discarded.

The predicted temperature change under the A1T scenario averages out at 2.4 degrees C, with the various climate models producing a range of predictions between 1.4 and 3.8 degrees C. The predicted temperature change under the A1B scenario averages out at 2.8 degrees C, with the various climate models producing a range of predictions between 1.7 and 4.4 degrees C. In both cases the uncertainty is of the same order as the 'most likely' temperature change. There is still an awful lot of 'noise' being produced by the global climate models.

5 comments:

Anonymous
said...

Let's cut to the chase: are we up a creek that is very likely not to be a creek by the time our kids' lives get messy? On the way into work this morning, my wife and I discussed a wide range of issues: our childcare arrangements, my smoking in the car, the traffic, politics, what we'd do if we won the lottery and, of course, global warming. I couldn't help but wonder is it asking too much of most people to be able to think about so many things almost simutaneously and to act rationally and responsibly in each case (for example, I'm not giving up the fags). Moreover, I'm not sure human beings are very well suited to thinking globally, or certainly not to acting globally in their day-to-day lives. But isn't that what we need to start doing? It doesn't augur well, methinks.

PS. I am trying to follow some of your posts, despite my ignorance, although you lost me with the formula one stuff.

A wonderful post anonymous! Reveal yourself!. Sorry about the F1 stuff, but it is part of my remit.

Are we up a creek or not? I honestly don't know. There was a chap interviewed on Newsnight last night who declared that the only people who now challenge the reality of anthropogenically driven global warming are ideologically driven, rather than analytically driven. In the case of people with interests in the oil industry, of course, this is probably true. But I think most people concerned about the environment now accept that at least some of the current global warming has been driven by greenhouse gas emissions, and they want to know by how much, so that we can make an informed choice about how much we need to place taxes or quotas on greenhouse gas emissions, and whether it would be both more effective and less costly to our economies to simply pump more investment into solar energy research. To answer these questions you need a reliable prediction of global temperature, but the global climate models cannot yet provide this.

In the presence of uncertainty then, I suspect the rational course of action will be to hedge our bets.

Sorry about the anonymity - it was an accident. I'll maintain it for now, just for the hell of it. Suffice to say I contribute to Bryan's blog quite a bit and I don't like cricket. I suppose we should be hedging our bets in the absence of definitive data. But sufficient data, nonetheless, to know we need to do some things. However, it is the 'we' bit that I think is going to cause problems. And in a way, democracy itself. There are not too many national politicians I know of who would be willing to promote long-term, environmentally significant policies at the expense of their short-term political ambition. And most ordinary folks, like me, will just carry on doing what we do each day. For that reason, the EU and its faceless bureaucrats, may have a very useful role to play. Lots of us just shrug and accept EU laws, as if it operates outside our sphere of democratic influence. Normally, one would consider this a bad thing, but in this instance it may be good thing (as long as the EU acts appropriately!). Thanks for answering my late-at-night-feeling-insignificant-and-helpless-in-the-face-of-complexity-and-human-failing post.

So what you're suggesting Neil, is that having unaccountable politicians in the EU can actually be beneficial in this instance, because these are the only types of politicians who can think longer-term!

Unmasked! No that's not what I'm suggesting. Given that there are so many vested interests involved in this one, including the political establishments in each country, that in the short-term the EU might be usefully employed as a buffer between what is expedient locally and what is crucial globally. I'm just trying to see how it might be possible to get the ball rolling in some kind of significant way. Sorry I have to make some dinner.